Ultrastructural localization of monosaccharide residues on cerebral endothelium.

Biotinylated lectins were used to localize oligosaccharides on the luminal plasma membrane of endothelium of intracerebral cortical vessels. Binding of concanavalin A, wheat germ and Ricinus communis-I was observed on the endothelial luminal plasma membrane of cerebral arterioles and capillaries indicating the presence of alpha-D-mannosyl, alpha-D-glucosyl, beta-N-acetylglucosaminyl, sialyl, and beta-D-galactosyl residues. Lectin binding occurred on the plasma membrane of pinocytotic vesicles open to the vascular lumen and on membranes at the luminal end of interendothelial junctions but not on membranes within junctions. Higher concentrations of Ulex europaeus-I, soybean, and Dolichos biflorus agglutinins were required to demonstrate the alpha-L-fucosyl and alpha-N-acetyl-D-galactosaminyl residues. Pretreatment of brain slices with neuraminidase accentuated the staining produced by soybean agglutinin and resulted in exposure of peanut agglutinin-binding sites on endothelium of arterioles and capillaries. In this respect cerebral endothelium differs from noncerebral endothelium which binds peanut agglutinin without prior neuraminidase pretreatment. The role of these saccharide residues in endothelial permeability and charge remains to be determined.